2.3 Ensure regular scans for unauthorized applications

Information

This recommendation is find and report (audit) software on the system that has not been included in the TE (trusted execution) TSD (trusted signature database).

These entries establish a so-called AllowList Software not included on this AllowList should be generating a syslog and/or audit record whenever it is executed.

Trusted Execution (TE) is an AIX security component that can be used to monitor

unauthorized

software in real time.

Unauthorized

seems a clear definition, but how TE determines

unauthorized

may not be as clear.Simply put, the goal is that all software is on the AllowList If not, the software is

unauthorized

.AIX uses the term TROJAN (see below) to determine that an application is

unauthorized

.Software that does not require any special kernel privileges to run is also authorized

What is a Trojan?

For this benchmark we add the AIX concept of TROJAN as a definition of

unauthorised

. AIX defines Trojan anyexecutable not in the TSD with one or more of the following characteristics:

- uses either SUID or SGID
- is linked to a command in the TSD ( AllowList )
- is in the privcmds (aka RBAC definition, ie, may have kernel privileges).
- is linked to a command in the privcmds database.

Summary :On AIX the construct AllowList is implemented by the TSD. The clear advantage of an AllowList monitored by a system security component is that the system can enforce and/or report violations of AllowList in real-time.

This recommendation focuses on reporting violations of the AllowList A later recommendation (update or new version of benchmark) will have a Level 2 recommendation including

enforcing violations

.

Solution

This will be a manual process. The remediation is to find and remove the offending file (currently the reported file might be the artifact of another error - most common is a symbolic link that points at a non-existent object).

The starting point is running the same command from the AUDIT section:

trustchk -i -n tree / 2>&1 >/dev/null | grep untrusted

Line by line, verify the root cause and act (one of):

- remove the offending object
- remove SUID/SGID settings
- remove privcmds setting
- add to TSD aka AllowList

See Also

https://workbench.cisecurity.org/benchmarks/10385

Item Details

Category: CONFIGURATION MANAGEMENT, SYSTEM AND INFORMATION INTEGRITY

References: 800-53|CM-7, 800-53|CM-7(1), 800-53|CM-7(5), 800-53|CM-10, 800-53|SI-7, 800-53|SI-7(1), CSCv7|2.1, CSCv7|2.3, CSCv7|2.6, CSCv7|2.7

Plugin: Unix

Control ID: 16c373a372cd9521275f0342dfc1ce71d35c6614a1bb7a43f5cf62f1026a5e0b